_content/doc/go1.26: document that Wasm requires signext and satconv

For golang/go#75005.

Change-Id: I27a109596b9159028bd3f0f3da1ec61fb87c5c09
Reviewed-on: https://go-review.googlesource.com/c/website/+/733240
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

_content/doc/go1.26.md

diff --git a/_content/doc/go1.26.md b/_content/doc/go1.26.md
index 7361ef7..5d575bd 100644
--- a/_content/doc/go1.26.md
+++ b/_content/doc/go1.26.md
@@ -680,5 +680,14 @@
 
 The `linux/riscv64` port now supports the race detector.
 
+### WebAssembly {#wasm}
+
+<!-- CL 707855 -->
+
+The compiler now unconditionally makes use of the sign extension
+and non-trapping floating-point to integer conversion instructions.
+These features have been standardized since at least Wasm 2.0.
+The corresponding `GOWASM` settings, `signext` and `satconv`, are now ignored.
+
 [laelf-20250521]: https://github.com/loongson/la-abi-specs/blob/v2.40/laelf.adoc
 [rfc 9180]: https://rfc-editor.org/rfc/rfc9180.html